1. Industrial Field
This invention relates to a magnetic bearing device.
2. Prior Art
First, specific construction of a magnetic bearing device is generally described hereinafter with reference to FIG. 2 showing an embodiment of this invention. In the drawing, numeral 1 indicates a movable member of a soft magnetic substance, and numerals 2, 3 indicate first and second supporting members respectively disposed on opposite sides, putting the movable member 1 therebetween. Permanent magnets 4, 11 are respectively disposed in the first and second supporting members so that magnetic attractive force generated in the permanent magnets 4, 11 acts on the movable member 1 from both sides. Further, coils 7, 14 are respectively disposed in the supporting members, and the mentioned magnetic attractive force is increased or decreased by applying electric current to the coils 7, 14 so that magnetic flux is generated in the same direction as the magnetic flux of the permanent magnets 4, 11, otherwise in the reverse direction. To hold the movable member 1 at a reference position between the supporting members 2, 3 in such a manner as not to contact the supporting members, application of current to the coils 7, 14 is controlled so as to increase magnetic attractive force in the reverse direction of the displacement or decrease the force in the same direction as the displacement when the movable member 1 deviates from the reference position.
It may be also possible that the application of current to each coil 7, 14 is so arranged as to be separately controlled, in which case current is applied to only one of the coils while applying no current to the remaining coil. In such an arrangement, however, nonlinearity of unstable spring constant becomes extremely large with respect to positional relation between the movable member 1 and each of the supporting members 2, 3, and it is difficult to obtain sufficiently stable controllability. It is, therefore, conventional to adopt an arrangement in which both coils 7, 14 are connected in series to apply current simultaneously to the coils, so that magnetic flux in one coil is in the same direction as magnetic flux of one permanent magnet, while magnetic flux in the other coil is in the reverse direction of magnetic flux of the other permanent magnet. That is, control for holding the movable member 1 stably at the reference position is carried out by simultaneously increasing magnetic attractive force from a supporting member located in the reverse direction of displacement of the movable member 1 and decreasing magnetic attractive force from a supporting member located in the same direction as the displacement.
FIG. 3 shows a circuit diagram of the above-mentioned arrangement for controlling current applied to both coils 7, 14, and in which numeral 41 indicates a drive circuit comprising a single-end-push-pull circuit, for example, and the mentioned coils 7, 14 connected in series join between the drive circuit 41 and a ground line 42. Connected to the drive circuit 41 are a positive (straight) polarity power source 43 and a negative polarity power source 44. Thus, in the detection of displacement of the movable member 1 from the reference position by means of a state detector circuit 45, either a current path from the positive polarity power source 43 to the earth line 42 as indicated by the solid line arrow in the drawing or a current path from the ground line 42 to the negative polarity power source 44 as indicated by the broken line in the drawing is alternatively established by means of the control circuit 46 in accordance with direction of displacement, whereby direction of current applied to the coils 7, 14 can be switched in accordance with direction of displacement of the movable member 1.
In the conventional control circuit of above arrangement, however, since the direction of current applied to the coils 7, 14 is switched in accordance with direction of displacement of the movable member 1 from the reference position, two power sources 43, 44 of positive polarity and negative polarity are essential. As a result, a problem exists in that the construction is large-sized, requiring a large manufacturing cost. In particular, when employing some backup battery to cover power supply interruption, at least two batteries are required respectively for the two positive polarity and negative polarity batteries 43, 44, resulting in further large-sized construction with more expensive manufacturing cost.